Jig device and apparatus and method of making a dental prosthesis or pattern therefor

ABSTRACT

A jig device holding a work piece is used with a milling machine that cuts from the work piece a prosthesis having a surface essentially free of defects. The jig device is inserted repeatedly into the machine in the same predetermined location, even upon inverting the jig device. This maintains the spatial relationship between the jig device and milling so, at start up, they are always in the same exact spatial relationship. The milling machine partially cuts through a first side of the work piece to form in the work piece a cavity having a surface part corresponding to at least a portion of the prosthesis being made. The jig device is then removed from the machine, inverted and reinserted into the machine at the same predetermined location. A support material is placed in the cavity prior to reinserting the jig device. Upon reinserting the jig device, the machine precisely cuts through an opposed side of the work piece to form within the work piece a prosthesis having a surface essentially free of defects. The prosthesis is supported within the work piece by the support material. The prosthesis and support material are separated to complete our method.

INCORPORATION BY REFERENCE

Any and all U.S. patents, U.S. patent applications, and other documents,hard copy or electronic, cited or referred to in this application areincorporated herein by reference and made a part of this application.

DEFINITIONS

The words “comprising,” “having,” “containing,” and “including,” andother forms thereof, are intended to be equivalent in meaning and beopen ended in that an item or items following any one of these words isnot meant to be an exhaustive listing of such item or items, or meant tobe limited to only the listed item or items.

In the claims, the words “prosthesis” or “prostheses” shall mean adental prosthesis or a pattern for making a dental prosthesis.

The word “rectangular” includes square.

The words “substantially” and “essentially” have equivalent meanings.

BACKGROUND

Computer technology has advanced to the point where a dental prosthesismay be milled from a solid block of material based on three-dimensionaldigital data corresponding to a proposed shape of the dental prosthesis.All methods of production begin with a model of the patient's dentition.The dentist will first make an impression of a patient's existingdentition, including the teeth immediately above and to the side of thetooth structure to which the dental prosthesis is to be attached. Afterfirst cutting away any unwanted tooth structure, thereby preparing thetooth to which the prosthesis is to be attached, the dentist has thepatient bite into an impression material forming a negative impressionof the patient's dentition. The negative impression is then filled withdental die stone to make a model. This model should duplicate theocclusion surfaces between upper and lower aligned teeth and theconfiguration of the prepared tooth structure to which the dentalprosthesis is to be attached. Currently there is a newer, less commonmethod of creating a model of the patient's dentition utilizing adigital impression. With digital devices placed in the mouth and usingcad/cam technology to produce the finished model, the need for aphysical impression is no longer there. Two such systems currently inuse in the United States would be the Itero System, manufactured byCadent and the C.O.S. System from 3M Corporation.

The computer aided design equipment used to make a dental prosthesis hasa scanner that is used to scan the surfaces of the model. Scanning maybe accomplished either with optical techniques using laser or non-laserlight or tactile techniques where a probe physically contacts theprosthesis's surface. The computer aided design equipment converts themodel's surfaces into three-dimensional digital data corresponding tothe physical shape of the model. This original data collected duringscanning is then used to create an image of the proposed shape for theprosthesis on a screen of a computer monitor. The original imagedisplayed on the monitor screen needs to be adjusted to modify theoriginal image to correspond to the ultimate shape of the dentalprosthesis. The computer aided design equipment is programmed to allowthe technician, with the aid of a mouse and employing conventional pointand click techniques, to change the shape of the image.

Because the data originally collected during scanning isn't preciseenough to make the dental prosthesis directly based on this data, thetechnician can and does make adjustments to the data originally providedby the scanner so that the dental prosthesis, at least in theory, fitsproperly into the patient's mouth. After making such adjustments to thedata collected by the scanner, the adjusted three-dimensional digitaldata is then forwarded to an automatic milling machine that then millsaway the unwanted material from a work piece to form the dentalprosthesis. Typically, the work piece is a block of material comprisedof ceramic, titanium, or a composite plastic material. Conventionalinvestment casting is also used to make a dental prosthesis and a waxpattern may be milled from a work piece of wax that is then used in theinvestment casting process.

SUMMARY

Our jig device and apparatus, and method of making a prosthesis, haveone or more of the features depicted in the embodiments discussed in thesection entitled “DETAILED DESCRIPTION OF SOME ILLUSTRATIVEEMBODIMENTS.” The claims that follow define our jig device and apparatusand method of making a prosthesis, distinguishing them from the priorart; however, without limiting the scope of our jig device and apparatusand method of making a prosthesis as expressed by these claims, ingeneral terms, some, but not necessarily all, of their features are:

One, in our method a milling machine mills from a two-sided work piece adental prosthesis essentially free of defects. The milling machine has acutting tool that terminates at a cutting tip that has, at a startposition, an exact spatial relationship with respect to a workingreference plane of the milling machine. A first side of the work pieceis presented to the cutting tool, and starting from the start position,the cutting tool is operated to partially cut through the first side toform in the work piece a cavity having a surface part corresponding toat least a portion of the prosthesis being made. A floor of the cavitymay include the surface part corresponding to at least a portion of theprosthesis being made. The work piece may be a substantially solid blockhaving opposed, substantially parallel, planar sides, and it may be madeof wax, metal, ceramic, or a plastic.

Two, the cavity is at least partially filled with a support material andthe work piece is inverted to present to the cutting tool a second oropposite side of the work piece. The work piece is inverted in a mannerso that the surface part corresponding to at least a portion of theprosthesis being made, namely, the cavity is in an exact predeterminedposition with respect to the working reference plane of the millingmachine. Starting from the start position, the cutting tool ispositioned to overlie the second side directly over and opposite anun-milled segment of the work piece that supports the surface partcorresponding to the partially milled prosthesis being made. When sopositioned, the cutting tool is now operated to completely cut throughthe second side of the work piece and form completely a prosthesis witha surface essentially free of defects. From each side of the work piece,the cutting tool may only cut into the work piece to a maximum depthcorresponding substantially to an optimum point of dissection of theprosthesis being made and no further. This defect free prosthesis issupported within the work piece by the support material, and theprosthesis is separated from the work piece as the final step in ourmethod.

Three, a jig device may be used to hold the work piece in the millingmachine at a predetermined location so the jig device and millingmachine are in an exact spatial relationship to enable the millingmachine to precisely mill from the work. Our jig device is detachablymounted to a planar tabletop of the milling machine and can be detached,inverted, and re-inserted after milling the first side of the work pieceinto the machine at the same predetermined location. The jig device andmilling machine may have interactive elements that enable the jig deviceto be repeatedly inserted, removed and inverted, and then reinsertedinto the milling machine at the same predetermined location with eachinsertion, or reinsertion after inverting. Thus, the jig device andmilling machine are always in the same exact spatial relationship toenable the cutting tool to precisely cut from the work piece aprosthesis having a surface essentially free of defects. The jig device,when inserted or reinserted into the milling machine, may be in a firstplane and the cutting tool may be at a right angle to this first plane.For example, our jig device when inserted or reinserted into the millingmachine may be substantially oriented in a horizontal plane and thecutting tool may be substantially oriented in a vertical plane.

In one embodiment, our jig device is substantially symmetrical about acentral longitudinal line and substantially symmetrical about a centrallatitudinal line. Our jig device may include a frame structure in whichthe work piece is seated, where the frame structure may have opposedplanar parallel surfaces that are, for example, spaced apart a distancesubstantially from ½ to 2 inches. There may be clamping means along theframe that keep the work piece in a stationary position within a spacein the frame structure and an alignment arrangement along the framemember that provides locating structure to enable the jig device toengage locating structure on the tabletop. The alignment arrangement maycomprise aligned openings positioned to intersect and engage a pair ofaligned vertical post elements projecting outward from the tabletopdirectly or indirectly by way of a platform fixedly attached to thetabletop. Each post element slides into an individual opening uponmounting the jig device to the tabletop. The clamping means may includea plurality of detachable members that upon being fastened to the framehold the work piece in the stationary position.

Four, our apparatus makes a prosthesis from a two-sided work piece, andit includes a milling machine and a holder for the work piece thatenables the work piece to be inverted. Our jig device and millingmachine have interactive elements that enable the jig device to berepeatedly inserted, removed and inverted, and then reinserted into themilling machine at the same predetermined location with each insertion,or reinsertion after inverting. Consequently, our milling machine may beprogrammed to operate so the cutting tool precisely cuts from the workpiece a prosthesis having a surface essentially free of defects. Thework piece is moved from a first position, presenting to the millingmachine's cutting tool a first side of the work piece, to a secondposition presenting to the cutting tool a second side of the work piece.A drive mechanism for the milling machine is initially operated when thework piece is in the first position so the cutting tool partially cutsthrough the first side of the work piece, to drill away a substantialportion of material from the work piece, while avoiding penetratingthrough the work piece with the tip of the cutting tool. This forms inone side of the work piece a cavity having a surface part correspondingto at least a portion of the prosthesis being made. The drive mechanismmay move the tabletop from the start position laterally along theworking reference plane in one or the other of orthogonal directions androtates and moves the cutting tool from the start position towards andaway from the tabletop along a straight line following the tool'slongitudinal centerline. The drive mechanism returns the cutting tooland the tabletop to their respective start positions after partiallycutting through the one side of the work piece to enable filling thecavity at least partially with the support material. The drive mechanismis operated to completely cut through the opposite side of the workpiece after filling the cavity with support material to finish making aprosthesis having a surface essentially free of defects.

In one embodiment of our apparatus, the milling machine's planartabletop may be mounted to move laterally in a straight line along theworking reference plane in one or the other of orthogonal directions.The cutting tool may be mounted to rotate and to move towards and awayfrom the tabletop along a straight line. The cutting tool's longitudinalcenterline may be normal to the working reference plane and intersects areference point on the working reference plane when the tabletop andcutting tool are in the start positions. A locating structure forpositioning the jig device in a predetermined location is on thetabletop. The locating structure enables an operator to manually insertthe jig device into the milling machine at a predetermined location sothe jig device and milling machine are in an exact spatial relationshipallowing the cutting tool to precisely cut from the work piece theprosthesis being made. This locating structure may comprise a detachableplatform including a pair of aligned vertical post elements projectingoutward from the tabletop. It may be designed to position the jig devicewith a surface of the jig device adjacent, and substantially parallelto, the planar tabletop.

These features are not listed in any rank or order nor is this listintended to be exhaustive.

DESCRIPTION OF THE DRAWING

Some embodiments of our jig device and apparatus, and method of making aprosthesis, are discussed in detail in connection with the accompanyingdrawing, which is for illustrative purposes only. This drawing includesthe following figures (Figs.), with like numerals indicating like parts:

FIG. 1 is a perspective view of partially formed prostheses milled froma work piece according to conventional milling processes.

FIG. 1A is a schematic flow diagram illustrating one embodiment of ourmethod of making a prosthesis.

FIG. 1B is a schematic diagram of computer aided design equipment usedin the making of a digitized image of a prosthesis.

FIG. 1C is a schematic cross-sectional view showing a wax pattern of acrown type dental prosthesis positioned in a casting ring used ininvestment casting.

FIG. 1D is a side elevational view of a patient's prepared toothstructure to which a crown type dental prosthesis made by our method isbeing attached.

FIG. 2A is an exploded perspective view of one embodiment of our jigdevice.

FIG. 2B is a perspective view of our jig device shown in FIG. 2A andassembled to hold a pair of wax work pieces.

FIG. 3A is an exploded perspective view of portions of our apparatuswith our jig device being attached to a tabletop of our apparatus.

FIG. 3B is a cross-sectional view of portions of our apparatus showingour jig device attached to the tabletop of a milling machine.

FIG. 4 is a cross-sectional view of portions of our apparatus showing acutting tool of our apparatus partially cutting into one side of a workpiece held by our jig device that is attached to the tabletop of theapparatus.

FIG. 4A is a perspective view of a rectangular work piece held by ourjig device shown in FIGS. 2A and 2B, showing side A of the work piece.

FIG. 4B is a perspective view of the rectangular work piece depicted inFIG. 4A inverted to show its side B.

FIG. 4C is an enlarged fragmentary cross-section view taken along line4A of FIG. 4.

FIG. 4D is a perspective view in phantom lines depicting athree-dimensional digital data image of a dental prosthesis stored inthe memory a computer.

FIG. 4E is a cross-sectional view taken along line 4E-4E of FIG. 4D.

FIG. 4F is a cross-sectional view taken along line 4F-4F of FIG. 4D.

FIG. 5 is a perspective view showing the one side A of the work pieceillustrated in FIG. 4A after being partially drilled to form a pluralityof cavities, each having a surface part corresponding to at least aportion of the prosthesis being made.

FIG. 6 is a cross-sectional view of the drilled work piece of FIG. 5filled with a support material.

FIG. 7 is a cross-sectional view similar to FIG. 4 with our jig deviceholding the drilled work piece filled with a support material, invertedand attached in the same location as depicted in FIGS. 3A, 3B, and 4,showing the cutting tool of our apparatus cutting into side B of thework piece to make a prosthesis having a surface essentially free ofdefects.

FIG. 8 is a top plan view of the work piece held by the jig device inthe inverted position illustrating the support material filling thecavities to support the completely milled prostheses that are suspendedwithin individual cavities.

FIG. 9 is a cross-sectional view illustrating separating the prosthesesmade by our method from the work piece.

FIG. 10 is a perspective view of one embodiment of our apparatuscomprising a conventional milling machine and our jig device (shown indotted lines) attached to a platform mounted to the tabletop of themilling machine.

FIGS. 11A through 11D are perspective views of another embodiment of ourapparatus where our jig device is mounted to be automatically rotated toinvert our jig rather than removed from our apparatus and manuallyinverted.

DETAILED DESCRIPTION OF SOME ILLUSTRATIVE EMBODIMENTS FIG. 1 Prior Art

The problem with conventional milling machines and methods for making adental prosthesis is the time consuming manual hand work required, aftercompletion of the milling process, to eliminate surface defects. Inorder to mill from a work piece 100 (FIG. 1) an object with an entirelycomplete organic shape (indefinable by a mathematical model) requiresthe milled object being manufactured to be physically suspended whileavoiding all contact with source material (wax, plastic, metal, etc.)from the work piece. Traditionally, milling any dental prosthesis fromany material requires support such as pins or positioning runners tohold the partially formed prosthesis in place while the prosthesis isbeing milled out of the work piece 100. Illustrated in FIG. 1 is amilled work piece 100 showing a number of dental prostheses 43 made inthe conventional manner and suspended within an opening 102 formed inthe body of the work piece. Arms 104 formed during milling extend acrossthe space of the opening 102 between each individual prosthesis 43 andthe body 100 a of the work piece 100 to keep the prostheses suspended inposition until a technician breaks the arms to detach each individualprosthesis from the body of the work piece. This leaves on eachindividual prosthesis residual surface defects that must be handpolished to eliminate. In such prior art manufacturing methods the workpiece is held immobile in the same stationary position throughout theentire milling process.

General

Our method avoids the formation of any residual surface defects on theprosthesis, thereby eliminating any hand working after milling a workpiece. In our method the prosthesis is manufactured in a completedthree-dimensional organic shape without using positioning pins or anypoint of attachment between the finished prosthesis and the body of thework piece. We are able to mill a completed three-dimensional organicshaped prosthesis by splitting in half a CAD/CAM milling patterncorresponding to the external and internal surfaces of the prosthesisbeing made. FIGS. 4D through 4F illustrate an exemplary milling patternMP in phantom lines representing a three-dimensional digital data imagestored in the memory a computer of a crown prosthesis 50 a.

Instead of keeping the work piece immobile through the entire millingprocess in our method about half of the milling pattern is milled in oneside of the work piece and the other half in the other side, each asindependent and separate operations. In other words, the prosthesis isformed in approximately half sections in two steps. To do this a workpiece is first milled from one side, and then the work piece is invertedto present for further milling from the opposite side of the work piece.We first establish and define the optimum point of dissection OPD (FIG.4D) of the milling pattern MP. The optimum point of dissection OPD isthe horizontal apex (determined by the milling instruction provided by amicroprocessor of a milling machine for any individual prosthesis beingmade) of any shape, and the maximum vertical limit of contact that canbe reached between source material provided by the work piece and thecutting tool of the milling machine. The optimum point of dissection OPDcan be compared to, and is similar to, the earth's equator. It is animaginary plane IP (FIG. 4D) that follows the outermost points along thecircumference of the prosthesis being made, essentially splitting themilling pattern MP into approximately half sections that are distortedhemispheres H1 and H2, each having a reference milling plane, namely,the reference milling plane RMP 1 for the hemisphere H1 (FIG. 4E) andthe reference milling plane RMP 2 for the hemisphere H2 (FIG. 4F). Theoptimum point of dissection OPD is mutually exclusive and unique to theindividual shape of the prosthesis being made, and therefore cannot bepredetermined or established until the milling pattern MP is complete asdiscussed subsequently in connection with FIG. 1B.

To mill a complete three-dimensional object such as a dental prosthesiswithout positioning pins or the like, starting at one of the referencemilling planes RMP1 or RMP2, we first cut into one side of the workpiece down to the optimum point of dissection OPD forming a cavity thatincludes a portion of the prosthesis being made. Once the optimum pointof dissection OPD has been reached, which corresponds to forming abouthalf the milling pattern MP, for example the hemisphere H2, the cavityis at least partially filled with the support material SM. This supportmaterial SM is a substitute for the milled away work piece material. Inour method, the support material SM filling the cavity acts like astationary sabot to hold the prosthesis being made immobile within thework piece, maintaining the prosthesis' exact position within the workpiece. The work piece may be held within a holding device that may berepositioned, exposing the opposite side of the work piece to thecutting tool.

Milling is continued with respect to the second reference milling planeRMP 2 by cutting into the opposite side of the work piece to form anobject corresponding to the other approximately half of the millingpattern MP, in this example the hemisphere H2. Milling from thereference milling plane RMP2 down to the optimum point of dissection OPDphysically separates the now completed milled prosthesis from the sourcematerial provided by the body of the work piece. The physical objectcorresponding to the milling pattern MP is now only held in place by thelateral pressure provided by the support material SM. With milling over,the completely milled prosthesis is separated from the support materialSM, free of any linear planes, positioning pin artifacts or moldingflash commonly found when using conventional methods. Using the supportmaterial SM as a “dental sabot” allows for full contour and completemilling of a finished prosthesis without hand finishing or removal ofpositioning pins and/or runners.

For example, our method and apparatus may be used to make a wax patternfor use in the lost wax process of making a dental prosthesis such asthe crown 50 a corresponding to the wax pattern 50. An example of asuitable work piece for use in the lost wax process is illustrated inFIGS. 4A and 4B and designated by the numeral 100′. This work piece 100′is a substantially solid block of wax having a planar side A (FIG. 4A)and opposed planar side B (FIG. 4B), which are substantially parallel.The work piece 100′ may have different shapes such as, for example,circular, rectangular, hexagonal, etc.

Lost Wax Process

As shown in FIG. 1B, a digital file of a three-dimensional image of thedental prosthesis is first made in accordance with conventionaltechniques from a model of a patient's dentition. A model 10 of apatient's lower jaw dentition is shown in FIG. 1B. A patient's upper jawdentition model may also used to collect prosthesis surface data, but isnot shown. For purposes of illustration as shown in FIG. 1D a preparedstump 32 to which a crown type 50 a dental prosthesis is to be attachedincludes a drilled away portion 32 a. The model 10 includes a replicate32 a of the stump 32 to which the crown type dental prosthesis 50 a isto be attached.

As shown in FIG. 1B, computer aided design equipment 19 creates an imageof a dental prosthesis based on data collected from the model 10. Theequipment 19 includes an optical scanner 20 that scans the surfaces ofthe model of a patient's dentition by directing a beam of light from asource 17 at the model's surfaces, for example, at prosthesis surfacesof the model stump 32 a. The reflected light represents informationcorresponding to the contours of these surfaces. This information iscollected by a sensor 15 and then stored in the memory 22 of a computer24 as three-dimensional digital data. Various images of a dentalprosthesis are displayed on the screen 18 of a monitor 30 connected toan output 32 of the computer 24 based on the data originally collectedby the scanner 20. These images, and the corresponding data creatingthese images, are modified by the technician using conventional inputdevices such as a mouse 26 and keyboard 28 to interact with, and modify,the originally collected three dimensional digital data.

The numeral 12 a is an image displayed on the screen 18 corresponding tothe actual prosthesis structure that is to be attached to the stump 32(FIG. 1D) prepared by a dentist for a dental prosthesis. The image 12 ais created by optically scanning the surface of the replicate 32 a ofthe stump 32 and manipulating the collected information of the surfacecontours, creating the image 12 a in accordance with a program 24 a thatcontrols processing of the data by the computer 24. As depicted in FIG.1B, an image 12 a of the crown 50 a to be attached to the stump 32 isdisplayed on the monitor's screen 18. Through the use of the mouse 26and keyboard 28 the technician can change parameters such as die spacer,minimum thickness of the prosthesis, contact points, grooves, cuspoverlays and marginal ridges.

Using our apparatus as discussed subsequently, a wax pattern 50 (FIGS.1C and 8) of the prosthesis being made is first milled from a work piece100′ (FIGS. 4A and 4B) made of wax. This wax pattern 50 is based on thedata collected during optical scanning and is used in the conventionalinvestment casting process to make, for example, a crown type dentalprosthesis 50 a as illustrated in FIG. 1D. As shown in FIG. 1C, the waxpattern 50 is attached to a sprue 60 made of wax material. This sprue 60is mounted to a raised conical portion of a rubber base 62 and a metalring 64 lined with a sheet 68 of ceramic fiber paper that is seated onthe base. Preferably, a wax rod 70 extends from a side portion of thewax pattern 50 to the base 62. The hollow interior 64 a of the ring 64and base 62 is then filled with the investment material, for example, aplaster, that is allowed to dry. After drying the assembly of the base62, ring 64 and mounted wax pattern 50 is inverted and the base removed.The sprue 60 and wax pattern 50 are next removed by burning them away sothat the casting is formed with a hollow cavity (not shown) into which amolten metal or ceramic material is forced to form the crown 50 a.

FIGS. 1A Through 10

In our method a conventional milling machine 200 (FIG. 10) cuts from thetwo-sided work piece 100′ a prosthesis essentially free of surfacedefects. Model OM2 sold by Haas is an example of a three-axis machinethat may be used, however, up to six-axis machines may be used topractice our method. This machine 200 has a planar, horizontal tabletop202 and a vertically oriented cutting tool 204 above the tabletop. Thecutting tool 204 may be a drill including a drill bit 206 terminating ata cutting tip 206 a and detachably connected to a spindle 208. A drivemechanism 210 for the milling machine 200 rotates the spindle 208 andbit 206 (FIGS. 4 and 7) as a unit, moves the spindle towards and awayfrom the tabletop 202 along a straight line following the drill bit'slongitudinal centerline z, and concurrently moves the tabletop laterallyin a straight line along a working reference plane WRP (FIGS. 4A and 4B)in one or the other of the orthogonal directions x and y. In thisexample, the working reference plane WRP is coextensive with thetabletop 202. Both the cutting tool 204 and tabletop 202 have a startposition where the tip 206 a of the cutting tool has an exact spatialrelationship with respect to the working reference plane WRP of themilling machine 200. In the start positions for both the cutting tool204 and tabletop 202, the cutting tool's longitudinal centerline z isnormal to the working reference plane WRP and intersects a referencepoint a on the working reference plane. In making dental prosthesestolerances are typically controlled to within 0.001 inch.

As depicted in FIG. 4, side A of the work piece 100′ is initiallypresented to the cutting tool 204 and, starting from the start position,the cutting tool partially cuts through the side A to form in the workpiece one or more cavities 101 b′ having a surface part corresponding toat least a portion of the prosthesis being made. For example, in FIGS. 4through 9, crowns are being manufactured where each individual crown 50a is custom made to fit snugly on an individually prepared tooth stump(FIG. 1D). In the embodiments disclosed herein, and as best depicted inFIGS. 4 and 4C, a floor F of an individual cavity AA is a surface partcorresponding to at least a portion of the prosthesis being made.Referring to FIG. 4A, the milled side A has a plurality of cavities 101b′ formed therein with, for example, a cavity AA in the corner C1 and acavity BB in the corner C2. In the first stage of our method as depictedin this example, the entire interior surface S1 (FIG. 4C) of the crown50 a and part of the exterior surface S2 of the crown are milled intothe side A of the work piece 100′. Also formed during this first stageis a lower edge 50 b (FIG. 4C) of the crown 50 a, that is, the perimeteror margin defining an open mouth M of the base B of the crown. In oneembodiment of our method and apparatus, the milling machine 200 isprogrammed to cut into side A of the work piece 100′ to a maximum depthcorresponding to substantially the greatest diameter (optimum point ofdissection) of the prosthesis being made and no further. The cuttingtool 204 and tabletop 202 are returned to their start positions afterpartially forming the prosthesis.

As depicted in FIGS. 5 and 6, the cavities 101 b′ formed in the one sideA of the work piece 100′ are at least partially filled with a supportmaterial SM. As best shown in FIG. 6, the support material SM fills theinterior of the partially formed prosthesis and covers the open mouth M,typically filling the entire cavity up to about the surface of side A.The support material SM may be contained within a tube T and may bedispensed manually or automatically. This support material SM may be agel that hardens shortly after being deposited in the cavity, but is notan adhesive that binds to surfaces of the partially milled work piece100′. Consequently, the support material SM may be easily separated fromthe finished prosthesis, which will be free of surface defects. Asuitable support material SM is, for example, Elite HD sold by Zhermack.

As depicted in FIGS. 4B and 7, in the next stage of our method, the workpiece 100′ is inverted to present to the cutting tool 204 the secondside B of the work piece 100′. The work piece 100′ is inverted in amanner so that the surface part corresponding to at least a portion ofthe prosthesis being made is in an exact predetermined position withrespect to the working reference plane WRP. Referring to FIG. 4A, in thestart position the side A lies in the working reference plane WRP withthe centerline z of the bit intersecting point a, which corresponds tothe center of the work piece. Upon inverting, the work piece 100′ isrotated 180° about its centerline C. This repositions side B so it nowlies in the working reference plane WRP with its center remaining in thesame relative position with respect to the cutting tool 204 in the startposition so the centerline z of the bit 206 intersects the work piece'scenter at point a. In this inverted position as depicted in FIG. 4B, thecavity AA shown in dotted lines now faces downward with its mouth Madjacent the table top 202 and side A substantially parallel to thesurface 202 a of the table top 202. The corners C1 and C2 and cavitiesAA and BB therein are now repositioned but in precise predeterminedlocations with respect to the start positions of the cutting tool 204and tabletop 202. Consequently, the cutting tool 204 is moved from itsstarting position into an overlying orientation with respect to arepositioned cavity, for example, cavity AA. When the work piece 100′ isthus inverted, repositioning occurs so that the cutting tool 204 uponmoving from the start position is positioned to overlie the second sideB and aligned opposite a segment 103 integral with the body 100 a′ andhaving an internal surface contoured as an individual surface partcorresponding to at least a portion of the prosthesis being madeportion, for example, the floor F of the cavity AA. The drill bit 206 isadvanced by the drive mechanism 210 so the tip 206 a cuts into side Band mills away the segment 103 to form the top surface of the prosthesisbeing made, for example, the surface 105 of the crown 50 a. The cuttingtool 204 now completely cuts through the second side B of the work piece100′ so the prosthesis formed is suspended by the support material SMand its surface is essentially free of defects. At this stage of ourmethod as depicted in FIGS. 7 and 8, this prosthesis free of surfacedefects is supported within the work piece by the support material SM.The prosthesis free of surface defects is finally separated from thework piece 100′ and support material as depicted in FIG. 9. This may bedone manually or automatically.

Milling Machine and Jig Device Combination

As schematically illustrated in FIG. 1A, in one embodiment of ourapparatus designated by the numeral 400 (FIG. 10) a jig device is usedto hold a work piece. In one embodiment of our jig device designated bythe numeral 300 and shown in FIGS. 2A through 3B, a pair of two-sidedrectangular work pieces WP1 and WP2 is held in our jig device 300. Thejig device 300 and milling machine 200, each time at start up, are inthe exact same predetermined spatial relationship when cutting fromeither side of the work pieces WP1 and WP2. To achieve this the jigdevice 300 is fastened in the same predetermined location to thetabletop 202 each time a work piece is cut, regardless of the side ofthe work piece being milled. In accordance with our method, the cuttingtool 204 partially cuts through the one side of the work pieces WP1 andWP2 to form in the work pieces individual cavities, each cavity having asurface including only a portion of the prosthesis being manufactured.What fraction of or portions is determined on a case-by-case basisdepending on the specific configuration of the prosthesis being made.

The jig device 300 is detachably mounted on a platform 402 fixed to thesurface 202 a of the tabletop 202. After partially cutting through oneside of each work piece WP1 and WP2, our jig device 300 is removed fromour apparatus 400. The cavities formed in the work pieces WP1 and WP2may be filled with the support material SM prior to removing the jigdevice 300 from the milling machine or after removing the jig device 300from our apparatus 400. Support material SM is allowed to cure, ifnecessary, so it adheres with sufficient strength to the bodies of thepieces WP1 and WP2 to support the prostheses upon completion of themilling process. After the cavities formed in the work pieces WP1 andWP2 are filled with the support material SM, the jig device 300 is theninverted and reinserted into our apparatus 400. The cutting tool 204 ismanipulated by the drive mechanism 210 to complete cutting away materialfrom the two opposite sides of the work pieces WP1 and WP2, forming aseries of prostheses, each with a surface essentially free of defects asdiscussed above. The support material SM is manually removed to separatethe prostheses from the body of the work pieces WP1 and WP2.

Jig Device

As shown in FIGS. 2A and 2B, the jig device 300 includes a frame member302 that provides a pair of adjacent rectangular spaces 302 a and 302 binto which the two-sided work pieces WP1 and WP2 are individuallyinserted and fit snugly therein. In the embodiment illustrated, theframe member 302 is substantially rectangular with a pair of opposedears 304 a and 304 b along a longitudinal centerline q of the jig device300 and a pair of opposed planar parallel surfaces 306 a and 306 bspaced apart a distance substantially from 1 to 2 inches. An alignmentarrangement along the frame member 302 comprising aligned holes 308 aand 308 b along the centerline q of our jig device 300, one hole in eachear 304 a and 304 b. A central partition member 310 divides the frame302 into two rectangular spaces 302 a and 302 b substantially of thesame dimensions. For example, each spaces 302 a and 302 b defines anopen area substantially from 4.5 to 5.5 square inches. These spaces 302a and 302 b each have a rectangular ledge L1 and L2, respectively, whichis adjacent and substantially flush or level with the one surface 306 bof the frame member 302. The other surface 306 a of the frame member 302has a number of recesses 312 in which clamps 314 are fastened by screws316. Initially the clamps 314 are removed and the rectangular workpieces WP1 and WP2, each one having about the same dimensions as anindividual open space, are individually inserted into the spaces 302 aand 302 b. The ledges L1 and L2 support the inserted work pieces WP1 andWP2 and the clamps 314 are reattached to the frame member 302 by thescrews 316 to keep the work pieces in place throughout the millingprocess.

Apparatus

As shown in FIG. 10, the conventional milling machine 200 is modified byattaching to the tabletop 202 the platform 460, thus constructing ourapparatus 400. Prior to conducting our method, the milling machine iscalibrated (touching off) each time a drill bit 206 is coupled to thespindle 208 so the cutting tool 204 has at its start position an exact,predetermined spatial relationship with respect to the working referenceplane WRP of the milling machine. Consequently, the machine 200 may beprogrammed to precisely cut from both sides of the work piece accordingto the milling pattern MP of the prosthesis being made. Using theappropriate reference milling plane as a guide, cutting tool 204 cutsinto one side of a work piece to the optimum point of dissection OPD,the work piece is manually or automatically inverted, and then using theother reference milling plane as a guide, the cutting tool cuts into theother side of the work piece to the optimum point of dissection OPD.

As best illustrated in FIGS. 3A, 3B, and 10, our jig device 300 is heldin a stationary position on the tabletop 202 so it moves laterally alongwith the movement of the tabletop. Although our jig device 300 may befastened directly to the tabletop 202, in the one embodiment apparatus400, it is mounted to the platform 402 that is bolted to the tabletop202 in a precise fixed position on the tabletop. Aligned vertical postelements 404 a and 404 b project outward at a right angle from a flathorizontal surface 404 a (FIG. 3A) of the platform 402. These postelements 404 a and 404 b interact with the alignment holes 308 a and 308b in the frame member 302, so an individual post element slides into anindividual hole, hole 308 a or 308 b, as the case may be, when our jigdevice 300 is mounted on the platform 402. In the embodiment depicted,the tabletop 202 has parallel T-slots 203 (FIG. 10) that provide a trackfor individual bolts 205, each bolt having a head 205 a that slidesalong a selected T-slot. Threaded shafts 205 b of these bolts 205 extendoutward from the surface of the tabletop 202 through orifices 402 a and402 b in the platform 402. When the platform 402 has been positioned onthe tabletop 202 in a precise location for proper calibration, nuts (notshown) are screwed onto the threaded shafts extending through theorifices 402 a and 402 b to lock the platform in position. Thisalignment arrangement enables the jig device 300 to be preciselypositioned on the tabletop 202, which is critical in milling the workpiece so no surface defects are produced. As discussed above, thecutting tool 204 has at its start position an exact, predeterminedspatial relationship with respect to the working reference plane WRP ofthe milling machine 200. Consequently, the machine 200 may be programmedto precisely cut from the work piece a prosthesis having a surfaceessentially free of defects by cutting from both sides of the work piecefor each individual prosthesis being made.

With the cutting tool 204 in its start position and the jig device 300properly located on the tabletop 202, the drive mechanism 210 for themilling machine 200 is initially operated. With the work piece in afirst position presenting one side to the cutting tool, a substantialportion of material from this one side is drilled away while avoidingpenetrating through the work piece with the tip 206 a of the drill bit206. This forms in the one side of the work piece a cavity, which asdiscussed above, is at least partially filled with a support material SMbefore or after removing the jig device 300 from its mounting to theplatform 402. In this embodiment, our jig device 300 is manually removedand inverted and re-mounted to the platform to present the opposite sideof the work piece to the cutting tool 204 for milling.

Because the drive mechanism 210 returns the cutting tool 204 and thetabletop 202 to their start positions after partially cutting througheither side of the work piece, and because of the way in which the jigdevice 300 interacts with the post elements 404 a and 404 b, theinitiation of the milling operation when cutting into either side of awork piece always occurs with the work piece in an exact predeterminedposition, except flipped over. Consequently, the milling machine may beprogrammed to precisely mill both sides of the work piece to make aprosthesis free of surface defects. As illustrated in FIG. 10, anelectronic control system for the drive mechanism 210 of our apparatushas a programmable microprocessor MP.

FIGS. 11A Through 11D

In the embodiment shown in FIGS. 11A through 11D, a mounting mechanism400 is employed to carry our jig device 300 and rotated it when requiredto invert the work pieces as discussed above. In this embodiment our jigdevice 300 is not removed from our apparatus.

The mounting mechanism 500 includes a pair of spaced apart verticalposts 502 and 504 each including a spindle 506 (only one shown) towhich, respectively, the opposed ears 304 a and 304 b of the jig areattached. The drive mechanism 210 is operably connected to each of thespindles, for example, the spindle 506. Upon actuation of the drivemechanism 210, the spindle 506 rotates our jig through a 180° turn,inverting the jig.

SCOPE OF THE INVENTION

The above presents a description of the best mode we contemplate ofcarrying out our jig device and apparatus and method of making aprosthesis in such full, clear, concise, and exact terms as to enable aperson skilled in the art to make and use. Our jig device and apparatusand method of making a prosthesis are, however, susceptible tomodifications and alternate constructions from the illustrativeembodiments discussed above which are fully equivalent. Consequently, itis not the intention to limit our jig device and apparatus and method ofmaking a prosthesis to the particular embodiments disclosed. On thecontrary, our intention is to cover all modifications and alternateconstructions coming within the spirit and scope of our jig device andapparatus and method of making a prosthesis as generally expressed bythe following claims, which particularly point out and distinctly claimthe subject matter of our invention:

The invention claimed is:
 1. A method wherein a milling machine cuts aprosthesis from a two-sided work piece held in a jig device, said methodcomprising, in sequence, the steps of inserting the jig device holdingthe work piece into the milling machine at a predetermined location sothe jig device and milling machine are in an exact spatial relationshipto enable the milling machine to precisely mill from the work piece aprosthesis having a surface essentially free of defects, partiallymilling through a first side of the work piece to form in the work piecea cavity having a surface part corresponding to at least a portion ofthe prosthesis being made removing the jig device from the millingmachine and filling the cavity at least partially with a supportmaterial, presenting to the milling machine a second side of the workpiece by inverting the jig device and reinserting the inverted jigdevice into the machine at said predetermined location, milling the workpiece from said second side to form said prosthesis with a surfaceessentially free of defects, said prosthesis being supported within thework piece by the support material, and separating the prosthesis fromthe work piece, where the jig device and milling machine haveinteractive elements that enable the jig device to be repeatedlyinserted, removed and inverted, and then reinserted into the millingmachine at the same predetermined location with each insertion, orreinsertion after inverting, so the jig device and milling machine arealways in the same exact spatial relationship to enable the cutting toolto precisely cut from the work piece a prosthesis having a surfaceessentially free of defects.
 2. The method of claim 1 where the millingmachine is programmed to cut into the work piece a maximum depthcorresponding to substantially an optimum point of dissection of theprosthesis being made and no further.
 3. The method of claim 2 where thejig device is substantially symmetrical about a central longitudinalline and substantially symmetrical about a central latitudinal line. 4.The method of claim 1 where the jig device includes a frame structurethat holds the work piece.
 5. The method of claim 4 where the framestructure has opposed planar parallel surfaces.
 6. The method of claim 1where the work piece is a substantially solid block having opposed,substantially parallel, planar sides.
 7. The method of claim 6 where thework piece comprises a wax, metal, a ceramic, or a plastic.
 8. Themethod of claim 1 where the jig device when inserted or reinserted intothe milling machine is substantially oriented in a horizontal plane andthe cutting tool is substantially oriented in a vertical plane.
 9. Themethod of claim 1 where the jig device when inserted or reinserted intothe milling machine is in a first plane and the cutting tool is at aright angle to said first plane.
 10. The method of claim 1 where a floorof the cavity corresponds to the surface part corresponding to at leasta portion of the prosthesis being made.